In the field of technology of image capture devices, the image qualities achieved by digital camcorders and digital still cameras have been significantly improved, and the number of functions provided for a single image capture device has been rapidly increased, these days. A list of main indices indicating the image quality of a moving picture generated by any of these image capture devices includes the number of pixels per frame (i.e., the resolution), the number of frames per second (i.e., the frame rate), and the ratio of an image signal to noise (SNR). There are various levels of resolutions available from the number of pixels that is barely usable for a QCIF compliant TV phone to as high a resolution as more than 10 million pixels for a digital single-lens reflex camera. Likewise, there are a wide variety of frame rates from only several frames per second to perform the sequential shooting function of a digital still camera to at least 30 frames per second for camcorders (and even more than 1,000 frames per second for special-purpose high shutter speed cameras).
However, it is difficult to further increase the image data read rate for imagers (such as CCDs and CMOS image sensors) that are used extensively now in those image capture devices. That is to say, there is a certain upper limit to the image data read rate. That is why it is not easy to capture a moving picture with both the resolution and frame rate kept high.
A conventional device for capturing a moving picture with a high resolution and a high frame rate synthesizes together multiple fields of an image that have been read with the reading start points changed one field after another (which will be referred to herein as a “1 to n interlaced image” 171) into a single frame of image (which will be referred to herein as a “full-frame image” 172) as shown in FIG. 37. Patent Document No. 1 discloses a device for generating a high-resolution frame image based on the pictures that have been read by such a method by reference to the information about a motion between the fields.
The Nyquist rate of an image is determined by the spatial sampling rate, or the number of pixels, of an image. According to the three-line decimation technique shown in FIG. 37, a single frame image is formed of three fields. In that case, the number of lines per field becomes one third as large as that of each frame image. That is why the sampling rate of each field image perpendicular to the direction in which the lines run becomes one third as high as the sampling rate of the frame image in the same direction. The Nyquist rate is a half of the sampling rate. That is why the Nyquist rate of each field image perpendicular to the direction in which the lines run also becomes one third as high as the Nyquist rate of the frame image in the same direction.
If a frame image included high-frequency components, of which the frequencies are equal to or higher than the Nyquist rate of each field image, then the field image would have aliasing components. Such aliasing components are generally superposed as either disturbance or noise on the frequency components, of which the frequencies are equal to or lower than the Nyquist rate. However, it is known that if multiple images with such aliasing components and their relative positions corresponding to the shift between the images are known, then a resolution that is equal to or higher than that of each of such images can be restored by a so-called “super-resolution” technology. For example, if an object and a camera are standing still relative to each other, a frame image can be restored based on multiple field images. In that case, since the Nyquist rate of each field image is equal to or lower than that of a frame image, signal components, of which the frequencies are equal to or higher than the Nyquist rate of each field image, will be included in the field image as the aliasing components. For that reason, in the frame image restored, those aliasing components can be restored as high-frequency components, of which the frequencies are equal to or higher than the Nyquist rate of the field image.
Even in a situation where the relative positions of an object and a camera change with time, as long as the motion of the object as viewed from the camera can be tracked accurately, an image with high-frequency components can also be restored by taking that motion into account as well as in the situation where they are standing still.
Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2007-028208